This invention relates to a class of dispersants for nonaqueous systems which can disperse insoluble fine powders in nonaqueous liquids within a short period of time and thereby give dispersions showing good dispersion stability for a prolonged period of time without forming a so-called hard cake.
Furthermore, the invention relates to dispersants which, when fine pigments insoluble in organic liquids are dispersed in said organic liquids in the presence thereof, can provide dispersions particularly excellent in flowability and dispersion stability.
Nonaqueous fine powder dispersions are used in various fields of industry. In the fields of paints, pigments and printing inks, for instance, dispersion of pigments or paint components forms an important basic technology and surfactants are used for dispersibility improvement. Since pigments, resins and solvents have become diversified, pigments are reduced to fine powders and various dispersants are used selectively for various solvents.
In addition, commodity products which are essentially dispersions of fine powders, such as lubricants, metal powders, abrasives, fillers, extenders, sintering agents, electric conductors, pulverized solid fuels, agrochemicals, disperse dyes and microbicides, in nonaqueous liquids have been developed or are under development and require dispersants in most instances.
However, the conventional dispersants for dispersing fine powders in nonaqueous systems are not yet fully satisfactory in many cases from the dispersion stability viewpoint since they allow precipitation or separation of fine powder particles during long-term storage. Furthermore, while the conventional dispersants can give dispersion systems which are good and satisfactory as evaluated just after preparation thereof and, in some instances, can effectively reduce the viscosity of the systems, they can hardly prevent, in many instances, fine powder particles in said dispersion systems from precipitating and forming a hard and hardly redispersible precipitate, namely a hard cake. Generally, when the initial dispersibility is better, a harder cake tends to form.
On the other hand, pigments of practical use in various coating compositions, such as printing inks and paints, should be composed of fine particles so that they can have a high tinting power and give vivid color tones. Therefore, the step of dispersing fine powder pigments in nonaqueous organic liquids is an important step in the production of printing inks and paints. However, it is difficult to produce coloring material compositions excellent in flowability and storage stability by dispersing pigments in nonaqueous vehicles, in particular when the pigment concentration is high. It is known that problems are often encountered from the production process viewpoint and/or from the product quality viewpoint.
For example, dispersions containing a pigment composed of fine particles often have a high viscosity and cause remarkable viscosity increases in dispersing, stirring and mixing and during transfer and storage, for instance, and, in extreme cases, gel to such an extent that they are no longer usable. Furthermore, in mixed pigments, vehicle-pigment phase separation, precipitation, aggregation, and/or segregation may happen, leading, in some instances, to decreases in tinting power and/or luster and/or to poor leveling.
Coloring materials giving good coat films, such as printing inks and paints, contain finely dispersed pigments in high pigment concentrations. For the production of dispersions containing finely divided pigments in such high concentrations, it is necessary to loosen and unbind particles that have aggregated and at the same time maintain dispersion stability by using dispersants and/or the like.
For these purposes, various dispersants for pigments have heretofore been disclosed. However, none is fully satisfactory from the performance viewpoint as a dispersant for pigments. The dispersants for pigments as disclosed in Japanese Kokai Patent Publication No. 59-227951, for instance, are colored and therefore suited for use only with certain kinds of pigment. They can never serve as general-purpose dispersants. As other dispersants known for the above purposes, there may be mentioned polyesters derived from hydroxycarboxylic acids by dehydration condensation (Japanese Patent Publication No. 54-34009), reaction products from such polyesters and polyethylenimines (Japanese Patent Publication No. 63-30057), reaction products from such polyesters and polyoctamethylenepolyamines (Japanese Kokai Patent Publication No. 62-4433) and compounds derived from polyalkylenimine-epoxide reaction products by further reaction with polyesters (Japanese Kokai Patent Publication No. 63-12335), among others. However, although they exhibit dispersing effect for a short period in weakly polar organic liquids, such as aliphatic hydrocarbon fractions and aromatic hydrocarbons, they are inferior in long-term storage stability. They cannot produce any dispersing effect in highly polar liquids, such as alcohols.